Reusable Launch Vehicle Control Research Articles

Design and Implementation of Continuous Bounded Finite-Time Attitude Control of Reusable Launch Vehicle

In this paper, a novel continuous bounded finite-time control algorithm is proposed for reusable launch vehicle (RLV) attitude control system with mismatched disturbances and unknown control coefficients. The remarkable feature of the developed algorithm is to ensure the finite-time stability of RLV attitude system with uniformly continuous bounded control torque signal. Meanwhile, a multivariable finite-time observer is designed to estimate the unknown mismatched disturbances, and the combination of the developed controller and observer could offer better robustness without losing control boundedness. Finally, numerical simulations and experimental results based on three-axis turntable are provided to verify the effectiveness and advantages of the proposed continuous bounded finite-time control method.

Adaptive output feedback attitude control for reusable launch vehicle with input constraints and actuator faults

This paper considers an adaptive output feedback fault tolerant control (FTC) for a reusable launch vehicle (RLV) during reentry phase for which four grid fins are used as actuators. Based on a prescribed tracking performance and an auxiliary system to deal with the input constraints, the proposed adaptive controller can compensate for the effect of uncertainties, external and internal disturbances, input constraints and actuator faults. It is shown that with the proposed scheme, the system tracking performance can be guaranteed even in the presence multiple actuator faults. The influence of the input constraints on the tracking performance is also investigated. Simulation results are presented to illustrate the effectiveness of the proposed scheme.

Practical predefined-time barrier function-based adaptive sliding mode control for reusable launch vehicle

This paper proposes a novel barrier function-based adaptive sliding mode control scheme with practical predefined-time convergence for reusable launch vehicles subject to parametric uncertainties and external disturbances. Distinguished from existing similar works, the proposed control scheme ensures that the attitude tracking errors converge to a pre-assigned region in a prescribed time without any prior information on the lumped disturbance, and the control gain is not overestimated. Firstly, a novel performance function with quantitatively predefined convergence time and steady-state error is designed to constrain the attitude tracking errors, and the equivalent unconstrained transformation is carried out for the constrained model. Subsequently, a novel adaptive sliding mode controller is devised for the transformed system by synthesizing the integral sliding mode paradigm and the barrier function-based adaptive gain technique. The stability of the controller is analyzed by the Lyapunov method. Finally, comparative numerical simulation results are presented to demonstrate the effectiveness and improved performances of the proposed control scheme.

Resilient Composite Learning Neuro-Adaptive Integrated Guidance and Control for reusable Launch Vehicle

An integrated guidance and control system for tracking a reference flight path trajectory of a reusable launch vehicle in the presence of model uncertainties, external disturbances, and measurement noises is proposed. To achieve this goal, a properly-trained feedforward neural network to estimate uncertainties in conjunction with a disturbance observer, which estimates external disturbances and the estimation error made by the neural network, is implemented in both the guidance and control loops. In addition, a state observer is designed whose state estimation error is included (along with the tracking error) in the learning algorithm of the neural network and the disturbance observer; such learning is called composite learning. The combined neural network and disturbance observer (employed in both the guidance and control loops) can consistently compensate for complex uncertain terms in the dynamic model of a reusable launch vehicle. More specifically, the introduced design results in an asymptotic tracking of the reference command, thereby providing a resilient flight control system. Extensive simulations are performed to show the effectiveness and robustness of the proposed integrated guidance and control system for trajectory tracking in the presence of uncertainties, aerodynamic disturbances, and measurement noises.

Adaptive finite-time prescribed performance attitude tracking control for reusable launch vehicle during reentry phase: An event-triggered case

This paper is devoted to address the attitude tracking problem for reusable launch vehicle (RLV) with uncertain aerodynamic parameters, input saturation and limited transmission resources. Based on the framework of the backstepping technique, a novel event-triggered adaptive prescribed performance control protocol is presented. Firstly, an extended state observer is used to provide the estimation for the whole system uncertainties. Then, an event-triggered mechanism is applied to exactly determine when control signals should be updated, which successfully eliminates the unnecessary periodic/continuous sampling in time-triggered researches and creates less waste of transmission resources. To compensate the negative effects induced by the aperiodic updating of control signals in event-triggered mechanism, an appointed-time prescribed performance controller is devised. In this way, the stability and tracking performance for the attitude system of the RLV can be guaranteed simultaneously. Moreover, the detailed theoretical analysis confirms that Zeno-free triggering is completely guaranteed along with stability. Finally, extensive simulations are carried out to validate the effectiveness of the proposed control protocol.

Fixed-time disturbance observer-based nearly optimal control for reusable launch vehicle with input constraints

In this paper, a fixed-time disturbance observer-based nearly optimal control (FTDO-NOC) scheme is proposed for reusable launch vehicle (RLV) subject to model uncertainties, input constraints, and unknown mismatched/matched disturbances. The dynamics of RLV attitude motion are divided into outer-loop subsystem and inner-loop subsystem. For the outer-loop subsystem, to address the problems of unknown mismatched disturbances and model uncertainties, a novel adaptive-gain multivariable generalized super-twisting (AMGST) controller is proposed. Two modified gain-adaptation laws are derived for tuning the control gains of AMGST controller, which attenuates chattering efficiently. For the inner-loop subsystem, considering the effect of unknown matched disturbances, a fixed-time disturbance observer (FTDO) is utilized to estimate the matched disturbances and the time derivative of virtual control input. Incorporated with the designed FTDO, a nearly optimal controller (NOC), which is based on the critic–actor neural networks (NNs), is utilized to generate the approximate optimal control moments satisfying the input constraints. The tracking errors of inner-loop subsystem and the weight estimation errors of the critic–actor NNs are proved to be uniformly ultimately bounded (UUB) via Lyapunov technique. Finally, we provide simulation results to validate the effectiveness and superiority of the proposed control scheme.

Accelerated Landweber iteration based control allocation for fault tolerant control of reusable launch vehicle

This paper presents a novel Fault Tolerant Control (FTC) scheme based on accelerated Landweber iteration and redistribution mechanism for a horizontal takeoff horizontal landing reusable launch vehicle (RLV). First, an adaptive law based on fixed-time non-singular fast terminal sliding mode control (NFTSMC), which focuses on the attitude tracking controller design for RLV in the presence of model couplings, parameter uncertainties and external disturbances, is proposed to produce virtual control command. On this basis, a novel Control Allocation (CA) based on accelerated Landwber iteration is presented to realize proportional allocation of virtual control command among the actuators according to the effective gain as well as the distance from the current position of actuator to corresponding saturation limit. Meanwhile a novel redistribution mechanism is introduced to redistribute oversaturated command among healthy actuators (non-faulty or redundant). The proposed method can be applied to a real-time FTC system so that the controller reconfiguring is not required in case of actuator faults. Finally, the effectiveness of the proposed method is demonstrated by numerical simulations.

Fixed-time observer based fault tolerant attitude control for reusable launch vehicle with actuator faults

This paper focuses on the fault tolerant attitude control problem for the reusable launch vehicle (RLV) with model uncertainties, external disturbances and actuator failures/faults during the reentry phase. First, the kinematics and dynamics of the RLV are presented, and the control-oriented mode subject to actuator malfunction is established. Next, a novel fixed-time observer is designed to estimate the compound disturbances, including failure information and uncertainties. Specifically, the proposed observer can guarantee the estimation errors converging to zero within a settling time, which is independent with the system initial conditions. Based on the proposed observer, a finite-time fault tolerant attitude control scheme is developed based on the nonsingular terminal sliding mode technology, which would improve the reentry attitude tracking performance and ensure the finite-time stability of the closed-loop attitude control system even in presence of the actuator faults. Finally, the effectiveness of the proposed method is demonstrated by numerical simulations.

Nonsingular terminal sliding mode control for reusable launch vehicle with atmospheric disturbances

The controller design for reusable launch vehicles is challenging due to enormous amounts of model parameter uncertainties and atmospheric disturbances. This paper first derives six-degree-of-freedom model of a reusable launch vehicle with atmospheric disturbances. Next, four kinds of atmospheric disturbances are introduced and wind models are established respectively. For attitude control of the reusable launch vehicle, a nonsingular terminal sliding mode controller is designed with stability guaranteed. Finally, simulation results show a satisfactory performance for the attitude tracking of the reusable launch vehicle with atmospheric disturbances.

Finite-Time Reentry Attitude Control Based on Adaptive Multivariable Disturbance Compensation

The finite-time tracking control for reusable launch vehicle with unmatched disturbance is investigated. An adaptive-multivariable-disturbance-compensation scheme is proposed to provide the estimation for external disturbances where the bounds of the perturbations are not known. Based on the estimation, a continuous multivariable homogeneity second order sliding mode controller is designed to ensure that the attitude tracking is achieved in finite time. A proof of the finite-time convergence of the closed-loop system under the integrated controller and disturbance observer is derived using the Lyapunov technique. The features of the proposed control scheme are that it does not require any information on the bounds of the disturbance and its gradient except for their existence. At the same time, the finite-time convergence, nominal performance recovery, and chattering alleviation are guaranteed. Finally, some simulation tests are provided to demonstrate the effectiveness of the proposed control scheme.

Real-Time Trajectory and Attitude Coordination Control for Reusable Launch Vehicle in Reentry Phase

The real-time reentry trajectory and attitude coordination control for a reusable launch vehicle (RLV) is a very important and challenging problem. There are many aspects that make the research appealing, such as being able to autonomously replan a new trajectory onboard when the landing site is changed. In order to achieve the goal, an integrated guidance and control architecture is proposed in this paper. First, the offline reentry trajectory is designed based on adaptive Gauss pseudospectral method. Then, the obtained trajectory is used as the initial value guess for real-time reentry trajectory optimization. As a result, the pseudospectral-based optimal feedback reentry guidance is achieved via successive real-time optimal open-loop control which ensures that the guidance system has sufficient robustness for initial reentry perturbations. Furthermore, a multitime scale smooth second-order sliding-mode controller with disturbance observer is proposed to ensure the finite-time reentry attitude tracking despite the model parameter uncertainties and unknown external disturbances. Finally, two representative simulation tests are carried out to demonstrate the effectiveness of the proposed integrated guidance and control architecture for six-degree-of-freedom RLV.

Attitude control of reusable launch vehicle in reentry phase with input constraint via robust adaptive backstepping control

SummaryThe paper presents an attitude control problem of reusable launch vehicles in reentry phase. The controller is designed based on synthesizing robust adaptive control into backstepping control procedure in the presence of input constraint, model uncertainty, and external disturbance. In view of the coupling between the states of translational motion and the states of attitude motion, the control‐oriented model is developed, where the uncertainties do not satisfy linear parameterization assumption. The time derivative of the virtual control input is viewed as a part of uncertain term to facilitate the analytic computations and avoid the ‘explosion of terms’ problem. The robust adaptive backstepping control scheme is first proposed to overcome the uncertainty and external disturbance. The robust adaptive law is employed to estimate the unknown bound of the uncertain term. Furthermore, the attitude control problem subjects to input constraint is studied, and the constrained robust adaptive backstepping control strategy is proposed. Within the Lyapunov theory framework, the stability analysis of the closed‐loop system is carried out, and the tracking error converges to a random neighborhood around origin. Six‐degree‐of‐freedom reusable launch vehicle simulation results are presented to show the effectiveness of the proposed control strategy. Copyright © 2015 John Wiley & Sons, Ltd.

Integrated guidance and control for reusable launch vehicle in reentry phase

An integrated guidance and control scheme is developed for next generation of reusable launch vehicle (RLV) with the aim to improve the flexibility, safety and autonomy. Firstly, an outer-loop optimal feedback reentry guidance law with online trajectory reshaping capability is designed. Then, a novel reentry attitude control strategy is proposed based on multivariables smooth second-order sliding mode controller and disturbance observer. The proposed control scheme is able to guarantee that the guidance commands generated from the guidance system can be tracked in finite time. Furthermore, a control allocation is integrated in the system in order to transform the control moments to control surface deflection. Finally, some representative simulation tests are conducted to demonstrate the effectiveness of the proposed integrated guidance and control strategy for six-degree-of-freedom RLV.

Integrated Optimal Control of Reusable launch Vehicle and Actuation system using Linear Quadratic Regulator

Reusable Launch Vehicle (RLV) is used to carry payload from earth's surface to the outer space for more than once. The digital autopilot (DAP) used to control the RLV has an actuation system as its inner loop. The actuation system deflects the control surfaces (eg. fins) to bring about the necessary control action. The actuator is a complex system with many elements which work in co-ordination to bring about the necessary action. But in the design of autopilot, actuator is usually approximated as a second order system having the same bandwidth as that of the actual one. Due to this approximation, an understanding of the entire plant cannot be achieved. During implementation, the approximation of the order of the actuator may lead to deviation of the performance of the system from its specifications. It may also lead to unnecessary control of subsystems which would have been corrected without any control in an integrated model. In this paper, an integrated design of the RLV and its actuation system is developed. The actuation system consists of an electro hydraulic actuator and the associated elements. It is designed to actuate the booster fin of an RLV for the purpose of pitch control. The Linear Quadratic Regulator (LQR) control technique is used to design DAP for the integrated system. LQR is a modern control technique which ensures optimality in the design of the integrated system. A comparison of the performance of the integrated design of RLV and the design with an approximated second order actuator is made. The advantages of LQR technique over the conventional gain design technique are also mentioned.

Reusable Launch Vehicle Control Using Linear-Adaptive and Subspace-Stabilization Techniques

Reusable Launch Vehicle Control Using Linear-Adaptive and Subspace-Stabilization Techniques

Reusable Launch Vehicle Control in Multiple-Time-Scale Sliding Modes

A reusable launch vehicle control problem during ascent is addressed via multiple-time scaled continuous sliding mode control. The proposed sliding mode controller utilizes a two-loop structure and provides robust, de-coupled tracking of both orientation angle command profiles and angular rate command profiles in the presence of bounded external disturbances and plant uncertainties. Sliding mode control causes the angular rate and orientation angle tracking error dynamics to be constrained to linear, de-coupled, homogeneous, and vector valued differential equations with desired eigenvalues placement. Overall stability of a two-loop control system is addressed. An optimal control allocation algorithm is designed that allocates torque commands into end-effector deflection commands, which are executed by the actuators. The dual-time scale sliding mode controller was designed for the X-33 technology demonstration sub-orbital launch vehicle in the launch mode. Simulation results show that the designed controller provides robust, accurate, de-coupled tracking of the orientation angle command profiles in presence of external disturbances and vehicle inertia uncertainties. This is a significant advancement in performance over that achieved with linear, gain scheduled control systems currently being used for launch vehicles.

Ramjet-Powered Reusable Launch Vehicle Control by Sliding Modes

One possible approach to pitch control of an air-breathing reusable launch vehicle is differential throttling of opposite engines mounted on the conical lifting body. The vehicle must operate over a large range of  ight regimes. The problem is aggravated by the relatively large angle of attack, which produces nonsymmetrical engine operation. The dynamics of controlling supersonic compression inlets also requires very rapid response times. A pitch controller architecture is proposed based on the sliding mode control (SMC) approach. SMC is a robust, nonlinearcontrol techniquecharacterized by its total insensitivity to matcheddisturbances and its perfect rejection of unmatched disturbances. The pitch control of a conical reusable launch vehicle by opposite engines operating in ramjet mode is simulated. In response to pitch-induced disturbances, the SMC controller accurately tracks the prescribed nominal moment through generation of required engine thrust proŽ les. The control occurs in a minimum settling time with no chatter.

Entry Guidance and Trajectory Control for Reusable Launch Vehicle

An entry guidance concept, similar to that of the Space Shuttle, is considered for the reusable launch vehicle (RLV). But the reference trajectory deŽ ned by drag proŽ le is parameterized and optimized as piecewise linear functions of the energy. Analytical expressions for accurate downrange distance prediction and a performance index, theaccumulatedheat load,are obtained.A regularizationtechniqueisemployed toachievedesired properties of the optimal drag proŽ le. These results enable fast design of constrained optimal trajectories for both offline studies and possible onboard application. A nonlinear control law is derived for trajectory tracking, which guarantees globallyasymptoticallystable tracking of the reference drag proŽ le. Numerical results for a conceptual RLV are provided to demonstrate the optimal design of drag proŽ les and the performance of the trajectory control law under a variety of off-nominal conditions and navigationerrors in altitude rate.